This invention relates to veneer dryers and, more particularly, to a veneer dryer which utilizes radio frequency augmented with moderately hot, circulated air, to produce a faster drying time and more consistent uniform results than possible with known dryers.
Continuous veneer dryers, as presently known, ordinarily rely on circulated hot air to remove moisture from the wood and produce the drying action. Problems have been encountered in the use of conventional dryers. For instance, to obtain proper drying, many dryers require a large amount of floor space, which is undesirable. With the hot temperatures used for the air, scorching of the wood may occur. Volatiles which are released at higher temperatures are a problem. Dryer results are inconsistent, and highly dependant on the species and structure of the particular wood handled, and its moisture content.
This invention is based on the finding that very superior drying results are obtainable in a continuous veneer dryer, where radio frequency is relied upon to drive moisture carried internally in the wood to surfaces of the wood. With the moisture on the surface, the moisture is evaporated and removed by a stream of air which may be heated only to a moderate temperature. For instance, a temperature within the range of 250 to 350 degrees F. has been found highly satisfactory. Because of the use of radio-frequency energy, drying results are far less dependent on wood species, structure, and initial moisture conditions The use of only moderately heated air eliminates any tendency for scorching to occur. Further, over-drying is not a problem, and organic materials that volatilize at high temperature are not released. Dryer efficiencies are such that for a given volume of veneer, markedly less floor space for a dryer is required than is required for conventional type dryers.
Accordingly, an object of the invention is to provide an improved continuous veneer dryer, which utilizes radio frequency to liberate internal moisture and transport such to the veneer surfaces, with drying then being aided by the circulation of air at moderate temperature.
Another object is to provide a dryer which includes aluminum-surfaced conveyor and pressure-applying rolls for transmitting veneer through the dryer. By the use of aluminum, staining of the wood handled is minimized. With the presence of the pressure rolls, the veneer material is, in effect, subjected to an ironing action. Drying takes place with reduction of curling and deformation of the veneer.
A further object is to provide such a continuous veneer dryer, wherein radio-frequency electrodes utilized to subject the veneer material to radio-frequency energy take the form of aluminum electrodes distributed along the length of the dryer and interspersed with the conveyor rolls.
These and other objects and advantages are attained by the invention, which is described hereinbelow in conjunction with the accompanying drawings.